1. Field of the Invention
The present invention relates to a method for molding a cam ring with convex cams, a molding die assembly therefor, and a molded cam ring.
2. Description of the Related Art
For example, a conventional lens barrel is provided on its peripheral surface (inner and/or outer peripheral surface), with a cam ring having a convex cam. A molding die assembly to mold the cam ring from a synthetic resin material is moved in the axial direction of the cam ring. To this end, if a plurality of identical convex cams are provided on the peripheral surface of the cam ring, it is necessary to form the convex cams so as not to overlap each other at the ends thereof, with respect to the axial direction thereof. Namely, in the case of a cam ring having, on its peripheral surface, for example, four identical convex cams which are spaced from one another at an equal angular distance, if the length of each convex cam in the circumferential direction is greater than 90 degrees, it is impossible to part the molding die which is moved in the axial direction of the cam ring from the molded product.
Of course, even if the convex cams partly overlap at the ends thereof with respect to the axial direction of the cam ring, it is in theory possible to realize a molding die capable of parting, by providing a complicated split structure for the molding die assembly. In this case, however, parting lines of the molding dies are produced on the cam surfaces of the convex cam. A parting line on the cam surface makes the cam surface profile defective, and accordingly, such a method is undesirable.
It is an object of the present invention to provide a method and a die assembly for molding a cam ring having a plurality of convex cams whose ends overlap in the axial direction, wherein the cam ring can be molded without producing a parting line on the cam surface, and to provide a cam ring molded via such a method.
In order to achieve the above-mentioned objects, a method is provided for molding a cam ring from synthetic resin, the cam ring being provided on the peripheral surface thereof with a plurality of convex cams whose shape in a developed view is non-linear so that an angle defined between a tangential line on each convex cam and a plane including an axis of the cam ring is smoothly varied, the convex cams overlapping each other at the ends thereof as viewed in the axial direction of the cam ring, wherein a first cylindrical split molding die having a cam forming surface corresponding to one of front and rear cam surfaces of the convex cams, and a second cylindrical split molding die having a cam forming surface corresponding to the other of the front and rear cam surfaces of the convex cams are provided. The method includes setting the first and second cylindrical split molding dies so that the respective cam forming surfaces are located in a normal molding position to mold the cam ring having the convex cams; and upon completion of a molding operation, rotating the first and second cylindrical split molding dies relative to each other and relative to the molded cam ring, in a direction of an angle not greater than the minimum angle defined between the tangential line on each corresponding the front and rear cam surfaces and the plane including the axis of the cam ring, to thereby part the first and second cylindrical split molding dies from the molded cam ring.
In an embodiment, the cam forming surfaces of the first and second cylindrical split molding dies and a plane which includes an axis of the cam ring and intersects the cam forming surfaces are perpendicular to each other.
According to an aspect of the present invention, a molded cam ring having convex cams can be provided, wherein the molded cam ring is produced by the above-described method.
According to another aspect of the present invention, a molding die assembly is provided, for molding a cam ring from synthetic resin, the cam ring being provided on the peripheral surface thereof with a plurality of convex cams whose shape in a developed view is non-linear so that an angle defined between a tangential line on each convex cam and a plane including an axis of the cam ring is smoothly varied, the convex cams overlapping each other at the ends thereof as viewed in the axial direction of the cam ring, the molding die assembly including a pair of cylindrical split molding dies having cam forming surfaces corresponding to front and rear cam surfaces of the convex cams, respectively; and oblique parting surfaces provided on the pair of cylindrical split molding dies respectively, the parting surfaces being oriented in a direction of an angle not greater than the minimum angle defined between the tangential lines on the front and rear cam surfaces and a plane including the axis of the cam ring. The oblique parting surfaces are entirely brought into surface contact with each other when the cam forming surfaces are located in a normal molding position, and the cylindrical split molding dies are relatively rotatable along the oblique parting surfaces.
In an embodiment, the cam forming surfaces of the cylindrical split molding dies and a plane which includes an axis of the molded cam ring and intersects the cam forming surfaces are perpendicular to each other.
According to an aspect of the present invention, a molded cam ring can be produced by the above-described molding die assembly.
According to another aspect of the present invention, a cam ring molded from synthetic resin is provided, having on the peripheral surface thereof a plurality of convex cams whose shape in a developed view is non-linear so that an angle defined between a tangential line on each convex cam and a plane including an axis of the cam ring mold is smoothly varied, the convex cams overlapping each other at the ends thereof as viewed in the axial direction of the cam ring, wherein a parting line is not produced on the cam surfaces of the convex cams by split molding dies which are used to form the cam ring mold.
In an embodiment, cam forming surfaces of the split molding dies and a plane which includes an axis of the molded cam ring and intersects the cam forming surfaces are perpendicular to each other.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-241719 (filed on Aug. 9, 2000) which is expressly incorporated herein by reference in its entirety.